Channel rank feedback in multiple-input multiple-output communication systems

ABSTRACT

Embodiments of a system and methodology are disclosed for aperiodic (i.e., non-periodic) feedback of channel-side information, such as channel rank information, to a base station by having the receiver/UE initiate the feedback instead of using a scheduled feedback approach. The autonomous feedback of channel-side information may use one of several different types of physical channel structures for uplink scheduling requests, such as those being discussed for inclusion in the emerging LTE platform standard.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/020,596, filed Jan. 11, 2008, entitled“Channel Rank Feedback in Multiple-Input Multiple-Output CommunicationSystems,” and is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed in general to the field of informationprocessing. In one aspect, the present invention relates to a system andmethod for transmitting channel rank feedback information from one ormore receivers.

2. Description of the Related Art

Wireless communication systems transmit and receive signals within adesignated electromagnetic frequency spectrum, but capacity of theelectromagnetic frequency spectrum is limited. As the demand forwireless communication systems continues to expand, there are increasingchallenges to improve spectrum usage efficiency. To improve thecommunication capacity of the systems while reducing the sensitivity ofthe systems to noise and interference and limiting the power of thetransmissions, a number of wireless communication techniques have beenproposed, such as Multiple input Multiple Output (MIMO), which is atransmission method involving multiple transmit antennas and multiplereceive antennas. Such wireless communication systems are increasinglyused to distribute or “broadcast” audio and/or video signals (programs)to a number of recipients (“listeners” or “viewers”) that belong to alarge group. An example of such a wireless system is the 3GPP LTE (LongTerm Evolution) system depicted in FIG. 1, which schematicallyillustrates the architecture of an LTE wireless communication system 1.As depicted, the broadcast server 28 communicates through an EPC 26(Evolved Packet Core) which is connected to one or more access gateways(AGW) 22, 24 that control transceiver devices, 2, 4, 6, 8, whichcommunicate with the end user devices 10-15. In the LTE architecture,the transceiver devices 2, 4, 6, 8 may be implemented with basetransceiver stations (referred to as enhanced Node-B or eNB devices)which in turn are coupled to Radio Network Controllers or access gateway(AGW) devices 22, 24 which make up the UMTS radio access network(collectively referred to as the UMTS Terrestrial Radio Access Network(UTRAN)). Each transceiver device 2, 4, 6, 8 device includes transmitand receive circuitry that is used to communicate directly with anymobile end user(s) 10-15 located in each transceiver device's respectivecell region. Thus, transceiver device 2 includes a cell region 3 havingone or more sectors in which one or more mobile end users 13, 14 arelocated. Similarly, transceiver device 4 includes a cell region 5 havingone or more sectors in which one or more mobile end users 15 arelocated, transceiver device 6 includes a cell region 7 having one ormore sectors in which one or more mobile end users 10, 11 are located,and transceiver device 8 includes a cell region 9 having one or moresectors in which one or more mobile end users 12 are located. With theLTE architecture, the eNBs 2, 4, 6, 8 are connected by an S1 interfaceto the EPC 26, where the S1 interface supports a many-to-many relationbetween AGWs 22, 24 and the eNBs 2, 4, 6, 8.

As will be appreciated, each transceiver device, e.g., eNB 2, in thewireless communication system 1 includes a transmit antenna array andcommunicates with receiver device, e.g., user equipment (UE) 15, havinga receive antenna array, where each antenna array includes one or moreantennas. The wireless communication system 1 may be any type ofwireless communication system, including but not limited to a MIMOsystem, SDMA system, CDMA system, SC-FDMA system, OFDMA system, OFDMsystem, etc. Of course, the receiver/subscriber stations, e.g., UE 15,can also transmit signals which are received by the transmitter/basestation, e.g., eNB 2. The signals communicated between transmitter 102and receiver 104 can include voice, data, electronic mail, video, andother data, voice, and video signals.

Various transmission strategies require the transmitter to have somelevel of knowledge concerning the channel response between thetransmitter and each receiver, and are often referred to as“closed-loop” systems. An example application of closed-loop systemswhich exploit channel-side information at the transmitter (“CSIT”) areprecoding systems, such as space division multiple access (SDMA), whichuse closed-loop systems to improve spectrum usage efficiency by applyingprecoding at the transmitter to take into account the transmissionchannel characteristics, thereby improving data rates and link SDMAbased methods have been adopted in several current emerging standardssuch as IEEE 802.16 and the 3rd Generation Partnership Project (3GPP)Long Term Evolution (LTE) platform. With such precoding systems, CSITcan be used with a variety of communication techniques to operate on thetransmit signal before transmitting from the transmit antenna array. Forexample, preceding techniques can provide a multi-mode beamformerfunction to optimally match the input signal on one side to the channelon the other side. In situations where channel conditions can beprovided to the transmitter, closed loop methods, such as MIMOpreceding, can be used. Preceding techniques may be used to decouple thetransmit signal into orthogonal spatial stream/beams, and additionallymay be used to send more power along the beams where the channel isstrong, but less or no power along the weak, thus enhancing systemperformance by improving data rates and link reliability. In addition tomulti-stream transmission and power allocation techniques, adaptivemodulation and coding (AMC) techniques can use CSIT to operate on thetransmit signal before transmission on the transmit array.

With conventional closed-loop MIMO systems, full broadband channelknowledge at the transmitter may be obtained by using uplink soundingtechniques (e.g., with Time Division Duplexing (TDD) systems).Alternatively, channel feedback techniques can be used with MIMO systems(e.g., with TDD or Frequency Division Duplexing (FDD) systems) to feedback channel information to the transmitter.

Current proposals for providing channel rank feedback in LTE systems useperiodic feedback methods for the downlink MIMO channel whereby thefeedback period is controlled by the base station and is signaled to theuser. However, there are several problems associated with periodicfeedback. For example, there are difficulties in regulating the feedbackperiod creating overhead loss in channel rank feedback and/or loss inperformance. Furthermore, delays in identifying changes in the rank ofthe downlink channel by the base station can lead to catastrophic(several in succession) errors, thereby severely degrading performance.

Another problem related to channel rank information in MIMO systems isthe uncertainty regarding whether a channel rank request sent by a UE isactually received by the Node B. In a MIMO system, when the UE feedsback the MIMO channel rank to the Node B, the Node B can always overridethe rank request and transmit to the UE at a lower rank. In this case,the UE does not know whether there was an error in channel rankfeedback, in which case it can reseed the rank feedback, or whether thetransmitter decided to override the rank request. In some MIMO systems,this lack of information may cause the UE to unnecessarily reseed therank feedback thereby increasing uplink overhead.

Accordingly, an efficient feedback methodology is needed to provide thechannel rank information to the transmitter while sustaining a minimalloss in link performance. In addition, there is a need for a methodologyto provide an indication to the UE of an override of a rank request.Further limitations and disadvantages of conventional processes andtechnologies will become apparent to one of skill in the art afterreviewing the remainder of the present application with reference to thedrawings and detailed description which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood, and its numerous objects,features and advantages obtained, when the following detaileddescription of a preferred embodiment is considered in conjunction withthe following drawings, in which:

FIG. 1 schematically illustrates The architecture of an LTE wirelesscommunication system;

FIG. 2 depicts a wireless communication system in which one or morereceiver stations autonomously feed back information to a transmitterstation for use in scheduling or otherwise preceding signaltransmissions by the transmitter station;

FIG. 3 illustrates an example signal flow for multiplexing autonomoususer feedback to a transmitter station;

FIG. 4 depicts an example channel rank physical resource map which maybe constructed and used at a controller to assign a specific combinationof signature sequence, frequency band and/or time interval to eachreceiver/UE device; and

FIG. 5 depicts an example flowchart for autonomously generating andfeeding back channel rank data for use in scheduling and AMC coding at atransmitter/base station.

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the drawings have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements for purposes of promoting andimproving clarity and understanding. Further, where consideredappropriate, reference numerals have been repeated among the drawings torepresent corresponding or analogous elements.

DETAILED DESCRIPTION

Embodiments of a system and methodology are disclosed for aperiodic(i.e., non-periodic) feedback of channel-side information, such aschannel rank information, to a base station by having the receiver/UEinitiate the feedback instead of using a scheduled feedback approach. Aswill be appreciated, the autonomous feedback of channel-side informationmay use one of the different types of physical channel structures foruplink scheduling requests, such as those being discussed for inclusionin the emerging LTE platform standard. At the base station, the feedbacksignal is received over one or more antennas, and the channel sideinformation is extracted and used to precode the transmission signals.For example, instead of using a scheduled channel rank feedback scheme,selected embodiments of the present invention allow the receiver/UE todetermine when channel rank feedback should be generated by using anyperformance-based metric, thereby reducing the average feedback rate. Insome embodiments, channel rank feedback information is generated andreported only when the receiver/UE determines that there has been asignificant change in the channel rank. However, if the receiver/UEdetermines that there has been no “significant” change in the channelrank, then no channel rank feedback is performed. In each of theembodiments described herein, the channel rank feedback information issent to the base station through the feedback control channel where itis processed to regenerate the original channel rank state informationand is used for scheduling and adaptive modulation control (AMC). Asused herein, channel rank is related to the number of parallel channelsavailable to transfer information between a base station and apredetermined UE. In various embodiments of the invention as describedherein, a channel rank feedback report from the receiver/UE will beunderstood to constitute a request by the receiver/UE to use apredetermined channel rank.

Various illustrative embodiments of the present invention will now bedescribed in detail with reference to the accompanying figures. Whilevarious details are set forth in the following description, it will beappreciated that the present invention may be practiced without thesespecific details, and that numerous implementation-specific decisionsmay be made to the invention described herein to achieve the devicedesigner's specific goals, such as compliance with process technology ordesign-related constraints, which will vary from one implementation toanother. While such a development effort might be complex andtime-consuming, it would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure. Forexample, selected aspects are shown in block diagram form, rather thanin detail, in order to avoid limiting or obscuring the presentinvention. In addition, some portions of the detailed descriptionsprovided herein are presented in terms of algorithms or operations ondata within a computer memory. Such descriptions and representations areused by those skilled in the art to describe and convey the substance oftheir work to others skilled in the art. Various illustrativeembodiments of the present invention will now be described in detailbelow with reference to the figures.

FIG. 2 depicts a wireless communication system 200 in which atransmitter station 202 communicates with one or more receiver stations204.i. With reference to the LIE wireless system depicted in FIG. 1, thetransmitter 202 may represent any of the control transceiver devices, 2,4, 6, 8 which act as a base station, while the receiver 204.i mayrepresent any of the end user devices 10-15. In the system 200 depictedin FIG. 2, one or more receiver stations 206.i autonomously feed backchannel rank information over a feedback channel 215 to a transmitterstation 202 for use in scheduling or otherwise precoding signaltransmissions by the transmitter station 202. As will be discussed ingreater detail hereinbelow, each receiver station 206.i monitors itschannel conditions and reports on a predetermined channel (such as aphysical LTE feedback channel that supports channel rank reporting) whenthere has been an important change in the channel rank conditions. Atthe transmitter 202, the random channel rank channel is decoded toextract the autonomously generated channel rank feedback information,which is used to configure or adapt one or more input signals that aretransmitted from a transmitter 202 (e.g., a base station) to one or morereceivers 206.1-m (e.g., subscriber stations). As will be appreciated,the transmitter station 202 and/or receiver stations 206.i include aprocessor, software executed by the processor, and other hardware thatallow the processes used for communication and any other functionsperformed by the transmitter station 202 and each of receiver stations206.i. It will also be appreciated that the transmitter station 202 canboth transmit signals (over the downlink path) and receive signals (overthe uplink path), and that each receiver station 204.i can receivesignals (over the downlink path) and transmit signals (over the uplinkpath).

The transmitter 202 includes an array 228 of one or more antennas forcommunicating with the receivers 206.1 through 206.m, each of whichincludes an array 209.i having one or more antennas for communicatingwith the transmitter 202. In operation, a data signal s_(i) presented atthe transmitter 202 for transmission to the receiver 204.i istransformed by the signal processor 226.i into a transmission signal,represented by the vector x_(i). The signals transmitted from thetransmit antenna 228 propagate through a matrix channel H_(i) and arereceived by the receive antennas 209.i where they are represented by thevector y_(i). For a MIMO channel from the transmitter 202 to the i^(th)receiver 206.i, the channel is denoted by H_(i), iε{1, 2, . . . , m}.The channel matrix H_(i) may be represented as a k_(i)×N matrix ofcomplex entries representing the complex coefficients of thetransmission channel between each transmit-receive antenna pair, where Nrepresents the number of transmit antennas in the transmit antenna array228, and k_(i) represents the number of antennas of the i^(th) receiver206.i. At the receiver 206.i, the signal processing unit 205.i processesthe y_(i) signals received on the k antennas to obtain a data signal,z_(i), which is an estimate of the transmitted data s_(i). Theprocessing of the received y_(i) signals may include combining the y_(i)signals with appropriate combining vector information v_(i) retrievedfrom the codebook 207.i or otherwise computed by the receiver's signalprocessing unit 205.i.

Precoding for downlink transmissions (transmitter to receiver) may beimplemented by having each receiver 206.i determine its MIMO channelmatrix H_(i)—which specifies the profile of the transmission channelbetween a transmitter and an i^(th) receiver—in the channel estimationsignal processing unit 205.i. For example, in a MIMO implementation,each receiver 206.1-m determines its MIMO channel matrix H_(i) by usingpilot estimation or sounding techniques to determine or estimate thecoefficients of the channel matrix H_(i). Each receiver 206.i uses theestimated MIMO channel matrix or other channel-related information(which can be channel coefficients or channel statistics or theirfunctions, such as a precoder, a beamforming vector or a modulationorder) to generate preceding information, such as preceding and powerallocation values, appropriate for the MIMO channel matrix. This may bedone by using the channel-related information to access a precoderstored in the receiver codebook 207.i. In addition, each receiver 206.iuses the estimated MIMO channel matrix or other channel-relatedinformation to generate channel rank information that is to be used toconfigure/adapt the signals transmitted by the transmitter.

In one embodiment, the autonomous channel rank report generator 201.imay include logic and/or circuitry for detecting a change in the mode ofoperation of the receiver 206.i (e.g., from a single-antenna mode ofoperation to a multi-antenna mode of operation) so that channel rankinformation is generated and reported to the transmitter 202 via thefeedback channel 215 only when such a mode change is detected.

Rather than feeding back the full channel rank representation, thereceiver 206.i may use a codebook 207.i to compress or quantize thetransmission profile (e.g., channel rank information) that is generatedfrom the detected channel information and that can be used by thetransmitter in controlling signal transmission to the receiver. Thechannel rank estimator 203.i generates a quantization/codebook index byaccessing the receiver codebook 207.i which stores an indexed set ofpossible transmission profiles and/or channel matrices H_(i) along withassociated channel rank information so that the estimated channel matrixinformation 204.i generated by the signal processing unit 205.i can beused by the channel rank estimator 203.i to retrieve a codebook indexfrom the codebook 207.i. The output of the channel rank estimator 203.iis provided to an autonomous channel rank report generator 201.i that isoperable to independently decide when to generate and feedback channelrank reports. For example, the autonomous channel rank report generator201.i may include a channel rank transition detector that detects achange in the channel rank information that meets a predetermined changethreshold requirement so that channel rank information is generated andreported to the transmitter 202 via the feedback channel 215 only whenthe predetermined change threshold requirement is met. In anotherexample, the autonomous channel rank report generator 201.i may includelogic and/or circuitry for detecting a change in the mode of operationof the receiver 206.i (e.g., from a single-antenna mode of operation toa multi-antenna mode of operation) so that channel rank information isgenerated and reported to the transmitter 202 via the feedback channel215 only when such a mode change is detected.

The autonomously generated channel rank information is transmitted viathe feedback channel 215 to the transmitter 202 where it may be storedand/or processed by the channel rank report detector/decoder 220. Forexample, a memory controller (not shown) in the channel rank reportdetector/decoder 220 may be used to update the previously reportedchannel rank information, either directly or using channel rankinformation retrieved from the codebook 222. In this way, the channelrank report detector/decoder 220 is operable to process the autonomouslygenerated channel rank information to provide channel rank informationthat can be used by scheduling module 224 and AMC selection module 225to generate scheduling or AMC information, respectively, for aparticular receiver 206.i. As will be appreciated, the scheduling module224 may be used to dynamically control which time/frequency resourcesare allocated to a certain receiver/UE 206.i at a given time. Downlinkcontrol signaling informs each receiver/UE 206.i what resources andrespective transmission formats have been allocated. The schedulingmodule 224 can instantaneously choose the best multiplexing strategyfrom the available methods (e.g., frequency localized or frequencydistributed transmission). The flexibility in selecting resource blocksand multiplexing users will influence the available schedulingperformance.

FIG. 3 illustrates an example signal flow for a user feedback procedurebetween one or more user devices 320 (such as a mobile device,subscriber station or other UE device) and a controller device 310 (suchas an eNB, controller or base station) which exchange messages usingprotocol stacks 316, 326 at the controller and user device,respectively. In accordance with selected embodiments, the UE 320includes a channel rank report module 321 which is used to autonomouslygenerate channel rank reports upon detecting important changes in thechannel rank information detected at the UE320. To the extent that thechannel rank report module 321 determines when channel rank reports willbe fed back to the controller device 310, the feedback may be consideredrandom or autonomous, as opposed to a scheduled or predetermined basisfor feeding back channel rank information.

Once the channel rank report module 321 determines that a channel rankreport should be fed back, the UE 320 must feed back the channel rankreport over an appropriate channel that supports UE-autonomous channelrank reporting. As described herein, the feedback channel, which isreferred to as the channel rank physical resource, is advantageouslyimplemented in whole or in part as part of the uplink control channel sothat multiple UE devices 320 can autonomously provide channel rankreports. For example, with LTE communications systems, the uplinktransmission scheme for FDD and TDD mode is based on Single CarrierFrequency Division Multiple Access (SC-FDMA) with cyclic prefix becauseSC-FDMA signals have better peak-to-power ratio (PAPR) propertiescompared to an orthogonal Frequency Division Multiple Access (OFDMA)signal. An example of an appropriate uplink channel is the SC-FDMAfeedback channel 330 depicted in FIG. 3. As depicted, the SC-FDMAfeedback channel 330 includes a central region of resource blocks thatdefine a data channel region 332 which is used to convey feedback data.In addition, the SC-FDMA feedback channel 330 includes edge of bandresource blocks that define dedicated control regions 331, 333 which areused to convey uplink control information, such as data non-associatedcontrol information. In accordance with selected embodiments of thepresent invention, the SC-FDMA uplink channel 330 is used to feed backchannel rank reports using the outer control channel frequencies 331,333. For example, by sending channel rank reports as part of the datanon-associated control information, the channel rank reports ofdifferent UEs can be multiplexed using the frequency/time/code domain ora hybrid of them within the assigned time-frequency region. With thisapproach, if the UE 320 has data to feed back, the channel rank reportcan be conveyed as data non-associated control information that is piggybacked on the data channel region 332. However, if there is no data tofeed back from the UE 320, the channel rank report can be conveyed asdata non-associated control information that is fed back in the outerfrequency regions 331, 333. As a result, channel rank reports may be fedback by a UE 320 using data non-associated control multiplexing withuplink data and without uplink data. In yet another embodiment, theremay be occasions when the UE 320 has an acknowledge/negative-acknowledge(ACK/NACK) signal to transmit on the uplink channel at the same time asa channel rank report (or other channel feedback information) is to befed back. By using the data non-associated control information for suchfeedback, the channel rank reports can be embedded, or “piggy backed,”in an ACK/NACK signal on an uplink channel. In various embodiments ofthe invention, rank feedback is signaled over the ACK/NACKchannelization by reserving at least one channelization for use of rankfeedback. This channelization corresponds to an a priori chosen set ofparameters including cyclic shift and orthogonal cover.

Various embodiments of the invention provide a methodology wherein abase-station/NodeB enabled to blindly decode rank information fromuplink control channel by searching for channel rank informationembedded in ACK/NACK or sounding reference signal (SRS) message, ordecoding it from a scheduling request message. Some embodiments of thepresent invention provide a UE-controlled channel rank methodology whichessentially modifies the current LTE structure for ACK/NACKtransmission. In various embodiments of the invention, this methodologycan be periodic or aperiodic. In an embodiment of the invention at leastone of the ACK/NACK channelizations are reserved for rank feedback whiletwo bits of information (4 possible ranks for 4×4 MIMO) are encoded withthe QPSK modulation symbol used for modulating the ACK/NACK sequences.By using this methodology, the channel rank feedback is at least asreliable as ACK/NACK feedback. In some embodiments, the channel rankfeedback is embedded in the downlink ACK/NACK transmission using thesame channelization. In another embodiment, the channel rank feedback isembedded in an uplink SRS signal using the same channelization. In thesetwo methodologies, extra overhead is eliminated by embedding channelrank information in a scheduled message. In some embodiments of theinvention, the channel rank feedback is embedded only if the UE electsto send a message. In yet another embodiment of the invention, channelrank feedback is encoded with an uplink scheduling request by the UE.The uplink scheduling request is necessarily tied to a UE ID messagesince it is transmitted on a random access channel.

The ACK/NACK and SRS messages are used in the aforementioned embodimentsbecause of reliability. Those of skill in the art will appreciate thatit is possible to embed the channel rank feedback information in othersignaling messages. Furthermore, those of skill in the art willappreciate that the three embodiments discussed above can be used inconjunction.

In various embodiments of the invention, rank feedback consisting of 1or 2 bits (2/4 possible ranks for 2/4 transmit antennas) is fed backusing QPSK symbols used for modulating the uplink control channelsequences. In some embodiments, a repetition factor of “two” is used inthe case of coverage limited UEs to ensure the same reliability forchannel rank feedback as for ACK/NACK. In embodiments implemented usingtwo transmit antennas, repetition is used to encode 1 bit in a QPSKsymbol. In embodiments implemented using four transmit antennas the 2bit is encoded in a QPSK symbol.

As described herein, the channel rank physical resource used to providechannel rank feedback may be directly assigned or broadcast to each UE320 by the controller 310, or may be indirectly derived at each UE 320.For example, the controller 310 may generate and broadcast asemi-statically assigned physical resource to define the uplink feedbackchannel which is used by all UEs 320 in the cell region to autonomouslyfeed back channel feedback information. The assigned physical resourcemay be used on a contention basis, on a synchronized RACH basis, on somehybrid basis or in any way desired to support random feedback over theuplink control channel. In selected embodiments, the channel rankphysical resources used by each UE 320 should be selected to promotemultiplexed feedback of channel rank reports. To this end, a channelrank physical resource module 312 at the controller 310 implements amultiplexing scheme by constructing and assigning a channel rankphysical resource over which the UEs 320 can multiplex feedbacksignaling information to the controller 310. In an exampleimplementation, the channel rank physical resource module 312 at thecontroller 310 uses code and/or frequency information to demultiplex thefeedback signaling information from the UEs 320, though otherdemultiplexing techniques may be used. However constructed, thedemultiplexing code and/or frequency information may be stored at thecontroller 310 in a data structure, such as a channel rank physicalresource map 313 in which distinct FDMA/CDMA codes are assigned to eachchannel rank physical resource. When the controller 310 identifies oneor more UEs 320 which are in communication with the controller 310, themap 313 may be populated with code and/or frequency information (e.g.,1st FDMA/CDMA Code) that the controller 310 uses to demultiplexautonomously generated channel rank reports that are fed back over thechannel rank physical resource in the uplink message 306 from the UEs320.

Once the controller 310 defines or specifies the channel rank physicalresource to be used for autonomous feedback by the UEs 320, the channelrank physical resource is included as access information in the downlinkmessage 301 that assigns the channel rank physical resource to the UE320. Using the assigned channel rank physical resource, the UE 320autonomously feeds back a channel rank report in an uplink message 307that is sent on a non-scheduled basis so that UE 320 determines whenfeedback is required. The autonomous nature of channel rank reportingmay be implemented by including at each UE 320 a channel rank reportmodule 321 that includes logic and/or circuitry for detecting importantchanges to the channel rank information or to the mode of UE operation.As channel rank reports are received at the controller 310, the channelrank physical resource module 312 decodes the channel rank reports usingthe code and/or frequency information (e.g., 1st FDMA/CDMA Code) that isstored in the map 313. The scheduling module 314 uses the assembledchannel rank information from the UEs 320 to generate scheduling or AMCinformation which is used to transmit downlink messages 309 to each UE320. For example, the scheduling module 314 can use the assembledchannel rank information for a variety of different purposes, includingtime/frequency selective scheduling, selection of modulation and codingscheme, interference management, and transmission power control forphysical channels (e.g., physical/L2-control signaling channels).

In another example embodiment, after the controller 310 assigns anddistributes the channel rank physical resource information forautonomous feedback of channel feedback information (with downlinkmessage 301), each UE 320 synchronizes with the downlink channel,transitions from an idle mode to a connected mode, and selects a randomaccess channel (RACH) feedback channel for communicating with acontroller 310 (or a network). To this end, each UE 320 includes a RACHselection module 322 for accessing a contention-based RACH in an SC-FDMAsystem. In operation, the RACH selection module 322 randomly selects aphysical resource for the RACH channel by obtaining RACH controlparameters after performing a successful cell search. The RACH selectionmodule 322 generates a RACH request which is included in the uplinkmessage 303. As needed, the RACH requests may be repeated as necessaryuntil the controller 310 returns an acknowledgement signal (ACK) or ano-acknowledgement signal (HACK) in a downlink message 305, signifyingwhether the RACH request is accepted. After an ACK signal is received ina downlink message 305, the UE 320 uses the previously-assigned channelrank physical resource to autonomously feed back channel feedbackinformation (such as a channel rank report) in an uplink message 307 byusing the channel rank report module 321 to determine when feedback isrequired. As channel rank reports are received at the controller 310,the channel rank physical resource module 312 is able to decode thechannel rank reports fed back over the channel rank physical resourcefrom the UEs 320. For example, once the controller 310 has received aRACH request 303 and acknowledged the request with an ACK signal 305,the channel rank physical resource module 312 has all the informationrequired to demultiplex and extract a channel rank feedback reportreceived over the channel rank physical resource, such as using a tablelookup or map 313. The scheduling module 314 uses the assembled channelrank information from the UEs 320 to generate scheduling or AMCinformation which is used to transmit downlink messages 309 to each UE320.

As described herein, the channel rank physical resources used by a UE320 to autonomously feed back channel rank information may beimplemented as a physical channel that is contention-based, or byexpanding the allocation of an existing synchronized random accesschannel. With contention-based feedback channels, there is always thepossibility that multiple UE devices 320 will be mapped to the samechannel rank physical resource, but this risk is deemed sufficiently lowbecause channel rank reports are fed back only when a UE 320 detects achange in the UE status and because the resource will be appropriatelydimensioned by the network. On the other hand, with synchronized RACHfeedback, each UE may be assigned a unique time slot so that each UEdevice 320 will be mapped to a unique channel rank physical resource.

FIG. 4 depicts an example channel rank uplink channel map 400 which maybe constructed and used at a controller 310 or UE 320 to specify achannel rank physical resource as a channel rank feedback channel from aparticular UE 320 in terms of a specific combination of signaturesequence, frequency band and/or time interval. In the depicted channelrank uplink channel map 400, each of eight uplink channels (#1-#8) isassigned a unique combination of signature sequence, frequency bandand/or time interval. In particular, the example channel rank uplinkchannel map 400 uses three dimensions (frequency, code and time) toassign a first code/frequency combination (Code 1, Frequency 1) tochannel rank uplink channel #1 at map entry 401, and to assign a secondcode/frequency combination (Code 4, Frequency 1) to channel rank uplinkchannel #2 at map entry 402. In addition, a third code/frequencycombination (Code 1, Frequency 2) is assigned to channel rank uplinkchannel #3 at map entry 403, a fourth code/frequency combination (Code3, Frequency 2) is assigned to channel rank uplink channel #4 at mapentry 404, and a fifth code/frequency combination (Code 4, Frequency 2)to channel rank uplink channel #5 at map entry 405. Finally, the mapassigns a sixth code/frequency combination (Code 1, Frequency N) tochannel rank uplink channel #6 at map entry 406, assigns a seventhcode/frequency combination (Code 2, Frequency N) to channel rank uplinkchannel #7 at map entry 407, and assigns an eighth code/frequencycombination (Code M, Frequency N) to channel rank uplink channel #8 atmap entry 408.

By constructing and maintaining the map 400 at the basestation/controller, channel rank reports that are received over theuplink can be demultiplexed and properly interpreted by the controllerto identify which UE devices are feeding back channel rank reports. Forexample, even though both channel rank uplink channel #1 and channelrank uplink channel #2 are assigned the same frequency (Frequency 1),they have the different code/frequency combinations by virtue of thedifferent assigned codes (Code 1 vs. Code 4). As a result, a channelrank report feedback message from a first UE on a first uplink channelcan be multiplexed in the same polling interval response with a channelrank report feedback message from a second UE on a second uplinkchannel, and the messages can be properly interpreted at the controllerby accessing the channel rank uplink channel map 400 to decode thechannel rank reports. As suggested by the channel rank uplink channelmap 400, it is possible to use only frequency assignments todifferentiate between different uplink channels, as shown by the factthat channel rank uplink channel #1, channel rank uplink channel #3 andchannel rank uplink channel #6 are distinctly designated in the map onthe basis of frequency only. Likewise, it is possible to use onlyCDMA-type coding assignments to differentiate between different channelrank uplink channels, as shown by the fact that channel rank uplinkchannel #1 and channel rank uplink channel #2 are distinctly designatedin the map on the basis of code only. However, by using code/frequencycombinations, more channel rank uplink channels can be readily anduniquely identified.

Referring back to the signal flow shown in FIG. 3, once a UE device 320receives or derives channel rank physical resource information anddetermines that a channel rank report needs to be fed back to thecontroller 310, the user device 320 sends the channel rank report in afeedback message 307 by using the specified channel rank physicalresource. Depending on the type of multiplex signaling information used,the channel rank report module 324 uses the multiplex signalinginformation to feed back the channel rank report in an uplink message307 that uses the assigned channel rank physical resource. Again, anydesired signaling scheme may be used for the feedback message 307,though in an example embodiment, the feedback messages are encoded andsent using the channel rank physical resource (e.g., in a dedicatedfrequency band of an uplink control channel).

The controller 310 may be implemented in the form of a correlatingreceiver which receives channel rank reports as feedback message(s) 307from the UE device(s) 320, where each channel rank report is encodedwith unique code/frequency combinations. When the code/frequencycombinations are selected to be non-interfering, a plurality of channelrank reports can be multiplexed and serviced together in the samepolling time interval using a simple physical layer signaling protocolto detect the presence (or absence) of channel rank reports.

FIG. 5 depicts an example flow for autonomously generating and feedingback channel condition information, such as channel rank data that isused for scheduling and AMC coding at a transmitter/base station. Themethodology starts (step 500) by autonomously generating and feedingback channel condition information (step 501) on a non-scheduled basis.A specific example of this step 501 is illustrated in FIG. 5 withreference to an example channel rank feedback flow which begins bydetermining the transmission profile for the MEMO channel or channelinformation to a given receiver station by using estimated channelinformation (step 502). Generally, an estimate of the channelinformation can be determined by embedding a set of predeterminedsymbols, known as training symbols, at a transmitter station andprocessing the training symbols at a receiver station to produce a setof initial channel estimates. In this example, the MIMO transmissionchannel being estimated at the receiver station may be characterized asa channel matrix H. The singular value decomposition (SVD) of the MIMOchannel matrix H=UΛV^(H), where the matrix U is a left eigen matrixrepresenting the receive signal direction, the matrix Λ represents thestrength (or gain) of the channel and the matrix V is a right eigenmatrix representing the transmit signal direction. However, it will beappreciated that any desired technique may be used to determine thetransmission channel profile, and that other profile determinationmethods can be used for other wireless systems in other embodiments.

Using the transmission profile, the receiver station generates thecurrent channel rank information (step 504). For example, a channel rankvalue may be generated by using the transmission profile information toaccess a quantization/codebook which stores an indexed set of possibletransmission profiles and/or channel matrices H_(i) along withassociated channel rank information. At this point in the process, thecurrent status of the receiver station (whether represented as quantizedchannel rank values or otherwise) has been determined. This currentstatus is compared to the previous status of the receiver station (step506) to see if there has been any change, such as by using a statetransition detector circuit or process. In accordance with variousembodiments of the present invention, if no change in the receiverstatus is detected (e.g., by comparing the current channel rank valuewith a previous channel rank value), the “same” outcome from decisionblock 506 is taken, in which case there is no channel rank report fedback to the transmitter station (step 508) and the process advances tostep 510 where any change in the status of the receiver station isdetected. As will be appreciated, the comparison that occurs at step 506can detect whether there is any change between the current and previouschannel rank values, or can detect whether there is any important changebetween the current and previous channel rank values, such as by using aminimum change threshold to quantify how much change must occur for achange to be detected. On the other hand, if the state transitiondetector detects a change in the receiver status (“different” outcomefrom decision block 506), then the receiver feeds back the channel rankreport to transmitter (step 512) using a physical channel that supportsautonomous channel rank reporting. In various embodiments, the channelrank feedback channel may be implemented as an LTE physical channel thatis contention based. Alternatively, the channel rank feedback channelmay be implemented by expanding the allocation of an existingsynchronized random access channel. At the transmitter station, thechannel rank reports are used to generate scheduling or AMC informationfor receiver stations (step 514), while the receiver station processadvances to step 510 where any change in the status of the receiverstation is detected. In this way, the process repeats so that thereceiver status (e.g., a channel rank report) is fed back to thetransmitter station only when the receiver station decides that thefeedback is required.

As discussed hereinabove, one of the problems related to channel rankinformation in MIMO systems is the uncertainty regarding whether achannel rank request sent by a UE is actually received by the Node B. Inparticular, when a UE feeds back the MIMO channel rank to the Node B,the Node B can override the rank request and transmit to the UE at alower rank. In this ease, the UE does not know whether there was anerror in channel rank feedback, in which case it can resend the rankfeedback, or whether the transmitter decided to override the rankrequest. In embodiments of the present invention, a Node B transmits achannel rank override indicator in the “ON” state to the user in a MIMOchannel in the case where it decides to use a different transmissionchannel rank than the channel rank recommended by the user. If the NodeB uses a different channel rank than the recommended rank and indicatesno rank override (or does not indicate rank override), the userconcludes an error in rank feedback and retransmits rank feedback.

By now it should be appreciated that there has been provided a methodand system for processing signals in a communication system byautonomously feeding back channel feedback information on anon-scheduled basis, where the channel feedback information may bechannel quality indicator information, rank adaptation informationand/or preceding matrix information, or an index representative of anyor all of the foregoing. As described, a first receiving deviceestimates channel state information for a transmission channel from atransmitting device to a first receiving device based on one or morereceived signals. The first receiving device then uses the channel stateinformation to generate channel feedback information for thetransmission channel to the first receiving device. Channel feedbackinformation will be fed back to the transmitting device over a randomaccess uplink channel in response to an autonomous determination by thefirst receiving device that channel feedback information should be fedback to the transmitting device. In this way, the amount of feedback maybe reduced as compared to scheduled feedback systems since the channelfeedback information is updated only when there are sufficient changesthereto. In addition, the amount of feedback may be reduced by changingthe size of a channel quality indicator report that is transmitted overa random access uplink channel to the transmitting device in response toa determination by the first receiving device that there has been achange in the channel feedback information for the first receivingdevice. For example, the channel feedback information can be transmittedas data non-associated control information over an uplink schedulingrequest channel or an LTE random access uplink channel, thereby allowingthe channel feedback information to be piggy backed on a data channelportion of a random access uplink channel, or allowing an ACK/NACKsignal to be piggy backed on the channel feedback information as datanon-associated control information on a random access uplink channel.The first receiving device can autonomously determine that channelfeedback information should be fed back by comparing current channelfeedback information to previous channel feedback information and/or bydetecting when the current channel feedback information exceeds ordiffers from the previous channel feedback information by apredetermined threshold amount. Alternatively, the first receivingdevice can autonomously determine that channel feedback informationshould be fed back by detecting a change in a mode of operation for thefirst receiving device. An example of such a mode change is switchingfrom a single antenna mode to a two antenna mode. The channel feedbackinformation can be fed back to the transmitting device over acontention-based RACH or a synchronized RACH, such as by using a datanon-associated control portion of a single carrier frequency divisionmultiple access (SC-FDMA) uplink channel. Once extracted from the uplinkchannel at the transmitting device, the channel feedback information maybe used to generate signal processing information to transmit data fromthe transmitting device to said first receiving device over thetransmission channel.

In another form, there is provided a receiver for use in a wireless LTEcommunication system. The receiver includes channel detection logic thatis operable to generate channel feedback information from transmissionchannel state information, where the channel feedback information may bechannel quality indicator information, rank adaptation informationand/or precoding matrix information, or an index representative of anyor all of the foregoing. The receiver also includes transmission logicthat is operable to transmit the channel feedback information inresponse to determining that there has been a change in the channelfeedback information for the receiver. The transmission logic determineswhether there has been a change in the channel feedback information bycomparing current channel feedback information to previous channelfeedback information, or by detecting when the current channel feedbackinformation differs from the previous channel feedback information by apredetermined threshold amount. The channel feedback information may betransmitted by the receiver using a synchronized random access channelor contention-based random access channel, such as may be provided inthe data non-associated control portion of a single carrier frequencydivision multiple access (SC-FDMA) uplink channel.

In yet another form, there is provided a method and system forprocessing signals in a communication system that includes a basestation and one or more UE devices, where the base station communicateswith each UE device over a respective transmission channel. Asdescribed, the base station receives channel feedback information thatis autonomously generated by a UE device on a non-scheduled basis, wherethe channel feedback information may be channel quality indicatorinformation, rank adaptation information and/or precoding matrixinformation, or an index representative of any or all of the foregoing.In operation, the base station broadcasts to the UE devices a physicalresource to be used for feedback of channel feedback information.Subsequently, channel feedback information is fed back to the basestation over the uplink channel using the physical resource from a UEdevice in response to a autonomous determination by the UE device thatchannel feedback information should be fed back. The channel feedbackinformation can be fed back to the base station over any an randomaccess uplink scheduling request channel or LTE uplink channel, such asa contention-based RACH or a synchronized RACH, by using a datanon-associated control portion of a single carrier frequency divisionmultiple access (SC-FDMA) uplink channel. In this way, the channelfeedback information can be piggy backed on a data channel portion of anuplink channel, or an ACK/NACK signal can be piggy backed on the channelfeedback information as data non-associated control information on arandom access uplink channel. Once extracted from the uplink channel atthe base station, the channel feedback information may be used togenerate signal processing information to transmit data from the basestation to said UE device over the transmission channel.

In yet another form, there is provided a multi-antenna transmitteroperable to indicate a channel rank override to a UE to indicate thatthe transmitter has transmitted at a different channel rank than thechannel rank recommeded by the UE. Furthermore, embodiments of theinvention provide a UE that is operable to decode the channel rankoverride indication (or the lack of it) according to the followingmethodology: (a) if the channel rank override indication is sent withvalue ON, then the UE decodes data according to transmitted channelrank; or (b) if the Node B uses a different channel rank than the UErecommended rank and indicates no rank override (or does not indicaterank override), the UE determines that there is an error in the channelrank feedback transmission and retransmits the channel rank feedback.

The methods and systems for autonomously generating and feeding backchannel-side information—such as channel rank information, rankadaptation information or MIMO codebook selection information—in alimited feedback system. as shown and described herein may beimplemented in software stored on a computer-readable medium andexecuted as a computer program on a general purpose or special purposecomputer to perform certain tasks. For a hardware implementation, theelements used to perform various signal processing steps at thetransmitter (e.g., coding and modulating the data, precoding themodulated signals, preconditioning the precoded signals, extractingchannel rank reports from the uplink messages and so on) and/or at thereceiver (e.g., recovering the transmitted signals, demodulating anddecoding the recovered signals, detecting changes in the receiver statethat require feedback of channel-side information, and so on) may beimplemented within one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, other electronic units designed to perform thefunctions described herein, or a combination thereof. In addition or inthe alternative, a software implementation may be used, whereby some orall of the signal processing steps at each of the transmitter andreceiver may be implemented with modules (e.g., procedures, functions,and so on) that perform the functions described herein. It will beappreciated that the separation of functionality into modules is forillustrative purposes, and alternative embodiments may merge thefunctionality of multiple software modules into a single module or mayimpose an alternate decomposition of functionality of modules. In anysoftware implementation, the software code may be executed by aprocessor or controller, with the code and any underlying or processeddata being stored in any machine-readable or computer-readable storagemedium, such as an on-board or external memory unit.

Although the described exemplary embodiments disclosed herein aredirected to various feedback systems and methods for using same, thepresent invention is not necessarily limited to the example embodimentsillustrate herein. For example, various embodiments of a channel rankfeedback system and methodology disclosed herein may be implemented inconnection with various proprietary or wireless communication standards,such as IEEE 802.16; 3GPP-LTE, DVB and other multi-user systems, such aswireless MIMO systems, though channel rank information can also be usedin non-MIMO communication systems. Thus, the particular embodimentsdisclosed above are illustrative only and should not be taken aslimitations upon the present invention, as the invention may be modifiedand practiced in different but equivalent manners apparent to thoseskilled in the art having the benefit of the teachings herein.Accordingly, the foregoing description is not intended to limit theinvention to the particular form set forth, but on the contrary, isintended to cover such alternatives, modifications and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims so that those skilled in the art shouldunderstand that they can make various changes, substitutions andalterations without departing from the spirit and scope of the inventionin its broadest form.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

1.-20. (canceled)
 21. A mobile device, comprising: a processor; awireless interface in data communication with the processor; and logicin data communication with the processor and the wireless interface, thelogic configured to cause the mobile device to: estimate channelinformation based on at least one received signal; determine a currentchannel rank indication based at least on part on the estimated channelinformation; compare the current channel rank indication against aprevious channel rank indication; and based at least in part on thecomparison, determine whether to transmit channel rank feedbackinformation relating at least in part on the current channel rankindication.
 22. The mobile device of claim 21, wherein the logic isfurther configured to transmit the channel rank feedback informationwhen the current rank indication is different than the previous channelrank indication.
 23. The mobile device of claim 21, wherein the logic isfurther configured to transmit the channel rank feedback informationwhen the current rank indication and the previous channel rankindication differ by at least a predetermined amount.
 24. The mobiledevice of claim 21, wherein the determination of whether to transmit thechannel rank feedback information is further based at least in part on achange in a mode of operation of the mobile device.
 25. A method ofoperating a mobile device, the method comprising: determining one ormore reception characteristics; determining a current rank indicationbased at least in part on the one or more reception characteristics;evaluating the current rank indication against a previous rankindication; and transmitting feedback information based at least in parton a determination that feedback information is to be provided to a basestation, the determination based at least in part on the act ofevaluating; wherein the feedback information is at least related to thecurrent rank indication.
 26. The method of claim 25, wherein feedbackinformation is transmitted based at least in part on a determinationthat the current rank indication differs from the previous rankindication.
 27. The method of claim 25, further comprising: Determining,subsequent to transmitting the feedback information, a new current rankindication; comparing the new current rank indication with the currentrank indication; retransmitting the feedback information when the newcurrent rank indication is different than the current rank indication.28. The method of claim 25, wherein the feedback information isconfigured to request a change in scheduling and/or adaptive modulationcontrol of signals transmitted to the mobile device by a base station.29. The method of claim 25, wherein a time for transmitting feedbackinformation is autonomously decided by the mobile device.
 30. Anon-transitory computer readable apparatus comprising a plurality ofinstructions configured to enable non-periodic feedback of channelinformation, where the plurality of instructions, when executed by aprocessor, cause a mobile device to: determine a transmission channelprofile based at least in part on channel estimate information; generatea current channel rank information based at least in part on thetransmission channel profile; and transmit feedback channel informationwhen the current channel rank information is determined to be differentfrom a previous channel rank information; wherein a time for thetransmission of the feedback channel information is autonomouslydetermined by the mobile device.
 31. A base station apparatus,comprising: a processor; at least one wireless interface in datacommunication with the processor; and logic in data communication withthe processor and the at least one wireless interface, the logicconfigured to cause the base station apparatus to: receive a channelrank request from a mobile device on a non-scheduled basis in responseto a determination by the mobile device; and schedule one or moreresources for the mobile device based at least in part on the channelrank request; wherein the determination by the mobile device is based atleast in part on a detection that a current rank request is differentthan a previous rank request.
 32. The base station apparatus of claim31, wherein the logic is further configured to: determine whether thescheduled one or more resources for the mobile device corresponds to arank level associated with the channel rank request; and when thescheduled resources do not correspond to the rank level, transmit anoverride indication to the mobile device, the override indicationconfigured to prevent a retransmission of the channel rank request bythe mobile device.
 33. The base station apparatus of claim 31, whereinthe logic is further configured to maintain a map of a plurality ofreceived channel rank requests from a respective plurality of mobilesdevices, the map configured to enable detection and decoding of theplurality of received channel rank requests.
 34. The base station ofclaim 33, wherein each channel rank request is assigned a uniquecombination of resources for which to use to transmit the respectivechannel rank request.
 35. A method for processing signals in a wirelesscommunications base station, the method comprising: receiving one ormore channel rank reports from respective one or more mobile devices;and assigning channel ranks to the one or more mobile devices; whereinthe one or more channel rank reports are transmitted by the respectiveone or more mobiles devices upon a determination by the respective oneor more mobile devices that a current rank level is different than aprevious rank level by a predetermined amount.
 36. The method of claim35, further comprising maintaining information relating at least in partto one or more resources used by the one or more devices to transmit therespective one or more channel rank reports.
 37. The method of claim 36,wherein the maintained information is configured to allow detection ofreceived one or more channel rank reports.
 38. The method of claim 35,further comprising transmitting an override indicator to respective oneor more mobile devices when the respective assigned channel rank isdifferent than a channel rank requested via the respective one or morechannel rank reports.
 39. A non-transitory computer readable apparatuscomprising a plurality of instructions for processing non-periodicfeedback of channel information, the plurality of instructions, whenexecuted by a processor, cause a base station to: receive a channel rankrequest from a mobile device, the channel rank request being generatedat least partly in response to when a determination is made by themobile device that a current rank level is different than a previousrank level by a designated amount.